Solipsism is the philosophical position that the only justified belief is that one's own mind exists. Anything external lacks absolute certainty and is thusly uncertain and untrustworthy. One's inability to determine whether or not he is in The Matrix is an example of this position.

Criticism

Absolute position is often rejected as meaningless. Lacking absolute certainty does not inhibit one from making consistently good decisions.

Whether or not one ascribes to the belief that he is in fact a brain in a jar does not affect his own feelings in the world he is experience, an illusion or not. It does not affect one's actions.